1. Field of the Invention
The present invention relates to the field of suspension thrust bearings used in particular in motor vehicles for the telescopic suspension struts of the steered wheels.
2. Description of the Relevant Art
A suspension thrust bearing generally includes an upper race and a lower race between which are arranged rolling elements in the form of balls or rollers. A suspension thrust bearing is generally arranged in the top of the suspension strut, between a suspension spring and an upper element secured to the body of the vehicle. The spring of the suspension device is installed around the rod of the damper piston, the end of which is secured to an elastic support block. The suspension thrust rolling bearing allows rotational movement between the support cup for the spring, which may rotate, and the elastic support block, which is fixed to the body of the vehicle. The relative angular movement between the support cup for the spring and the elastic block results from turning the steered wheel and/or from compression of the suspension spring. The suspension thrust bearing also allows axial forces to be transmitted between the spring and the body of the vehicle.
Thus Document FR-A-2 829 429 describes a suspension thrust bearing including a thrust rolling bearing, a support cup for a spring and an elastic support block. The rolling bearing includes an upper race arranged in an annular upper cap forming an interface between the upper race and the elastic block, and a lower race. Also provided is an annular lower cap forming an interface between the lower race and the support cup for the spring. One cap may include an elastic lip extending radially in the direction of a skirt of the other cap, forming a narrow passage and cooperating with a radial flange of the skirt, so as to allow axial movement in one direction while prohibiting reverse axial movement.
However, in many struts of recent design the springs have a complex shape and, after they have been fitted on the vehicle, exert an axial force which does not pass through the axis of the rolling bearing. The geometry of the spring is such that before it is preloaded and during the start of preloading, the end turns of the spring exert non-uniformly distributed and/or localized forces over a limited angular sector of the respective bearing points. This is therefore manifested at the upper end of the spring by the application of a non-uniformly distributed force on the lower cap of the thrust bearing. When the region on which the spring bears is situated radially outside the diameter over which the balls bear on the races, the concentration of the spring bearing forces on a region of the cap situated outside the bearing region of the balls may exert on the lower cap a tilting moment about the balls which causes partial unlatching of the two caps on the side diametrically opposite to the force application point.
The radial latching interference is in fact relatively small because it is only intended to provide axial retention for handling the caps. Since the caps are made of a relatively rigid synthetic material—often glass-fiber-reinforced nylon-6,6 polyamide—a large interference could cause unacceptable stresses on the material and local cracking or fractures.
When the final preload is exerted on the spring, the lower turn bears completely on the cup, which produces a modification of the orientation and of the distribution of the load exerted by the spring on the cap, which tends to close again.
After carrying out numerous tests, the Applicant noticed that when the two caps are disunited beyond a certain limit, the said caps do not generally return correctly into position, and local relative friction between the said caps subsequently occurs and this forms the basis of incorrect operation of the suspension thrust bearing with generation of noise and an excessive frictional torque.
The embodiments described herein aim to overcome these drawbacks.